This invention relates to a sprocket for a bicycle, which is formed of material, such as an aluminum alloy, having little wear-resistance, and more particularly to a sprocket for a bicycle, which comprises a main body with a large number of teeth circumferentially provided at the outer periphery of the body and is used mainly as a crank means for the bicycle.
Generally, the multi-stage sprocket of two or more sprockets with a different number of teeth is mounted to a rear hub or crank means of the bicycle so that a driving chain, which is moved axially of the sprocket by means of a derailleur is switched to a desired sprocket for transmitting the driving force to a rear wheel in a given speed change ratio.
The sprocket, when used for a crank means, is larger in diameter and has 40 to 50 teeth and is formed of a lightweight material, such as an aluminum alloy, for reasons of light weight and economy. The light material has less wear-resistance, so that the multi-stage sprocket of light material wears out its teeth, especially those which initially catch the chain when changing speed wear out to a greater extent, whereby its durability becomes a problem. When the sprocket is formed of a wear-resistant material, such as iron, to improve durability, the weight increases and it becomes expensive to produce. As a result, a sprocket having the advantages of lightweight material and free from the above defects has not been available.